I. Field of the Invention
The present invention deals generally with changeable message signs and particularly with self-powered, usually solar powered, portable signs of the class which are typically deployed as temporary road signs. The present invention offers reduced power consumption, enhanced visibility to intended observers, especially during the difficult hours about dawn and dusk, and improved automatic solar tracking and control in changeable message signs.
II. Related Art
Changeable displays or changeable message signs used for exhibiting visual or written information which are capable of portraying several sequential segments of information in a complete message and being further selectively programmable to display other messages have long been used to display real time information to motorists and assist in efforts to improve roadway operations and safety. These changeable message signs (CMS) have been used to inform and advise those using the highway of construction and maintenance circumstances together with even weather traffic or other highway conditions. Such displays generally have two distinct applications. The first relates to stationary changeable message signs which can be hard wired as permanent installations. The second covers portable signs or mobile units which are designed to be transported for use in remote locations, but which usually require some sort of power supply that is part of or travels with the unit.
In recent years, three main types of illumination for CMS displays have emerged as common and accepted modes. The first type is a light-reflecting type which uses light received from external sources such as the sun, automobile headlights or other illuminators exclusively to operate the message sign. While somewhat successful, these devices are quite limited in terms of visibility and usefulness and are the least adaptable to changing conditions.
A second type is exclusively light emitting in which light is provided on or behind the viewing surface within the sign housing. Selectively exposed areas define the desired messages. A third type employs a hybrid technique which combines aspects of both reflective and light emitting technologies in combination. The second and third type produce superior results when it comes to presenting a display which is highly visible under a variety of lighting conditions.
Portable changeable highway display signs typically form a display from an arrangement that consists of 24 available characters arranged in a configuration including 3 rows of 8 characters each. Each individual character is typically formed from a configuration of 35 pixels arranged in a 5.times.7 matrix. The entire arrangement, then, requires 840 operable pixels. By arranging a pattern in the pixels of each character across each row, a sign can be produced which easily displays a simple message. Each 5.times.7 pixel matrix, of course, can be patterned into any desired letter or number or operated to image part of a larger scene, such as a large arrow. Thus, the pixels of each character matrix can be changed so that any desired message or sequence of messages can be displayed.
Generally, for highway use, the message must be plainly visible from a minimum distance of 900 feet. This allows the typical motorist to have the sign in sight for just over 10 seconds while traveling 60 miles per hour (88 ft/sec). This 10-second time frame also permits the sign to change and display two to three sequences of simple messages or parts of a larger message with sufficient time to allow the additional information to be appreciated by the motorist.
With respect to portable systems, improvements that reduce power consumption are of great importance inasmuch as these systems cannot be hard wired to permanent electrical sources and must depend entirely on auxiliary or portable power generating sources for operation. Early portable display devices of the class were generally rather crude systems. They were large energy consumers that required rather large diesel or gasoline powered motor/generator (MG) sets to supply electricity. These units had to be transported with the signs and which required a great deal of supervision including periodic refueling. In addition to high electrical usage for illumination as by incandescent or fluorescent lighting, the early signs generally employed a large number of electro-magnetically operated mechanical shutters (one per pixel) which were pivotally operated between two stable positions, each exposing a side of the shutter.
Exemplary devices using mechanical shutters are shown and described in U.S. Pat. No. 3,975,728 to Winrow which discloses arrays of electro-magnetically operated pivotally mounted pixel elements each having a lighter and a darker side. Siebert et al (U.S. Pat. No. 4,389,804) also disclose the use of multi-position magnetically operable pivoting disks for each array. Cook et al (U.S. Pat. No. 3,507,057) disclose a device that includes a fibre optic illumination source in conjunction with magnetically operated indicator elements.
Because of the high cost of MG set generated power and because of advancements in energy conversion systems, solar power has become an important source of power generation for these portable signs in recent years. One such system is disclosed by Luoma et al (U.S. Pat. No. 5,542,203) which utilizes solar power generation in conjunction with illumination by light emitting diodes (LEDs) operated in conjunction with mechanical pixels. A photovoltaic powered optical shutter system for a reflective display is shown in U.S. Pat. No. 5,153,760 to Ahmad. Harris et al (U.S. Pat. No. 5,115,228) discloses a double-sided electro optic display in which shutters on either side of a central display allow different messages to be transmitted from opposed sides.
In addition, although solar power has been introduced with respect to the operation of mobile, changeable sign displays, the efficiency of the production and use of the solar energy has been quite limited. For example, crude mechanical or hand-operated adjustment techniques have been utilized to approximately position the solar panels with respect to the incident sunlight or, heat seeking devices have been utilized in an attempt to adjust the relative angle of the solar panels. Thus, there remains a need for an inexpensive but more effective method of positioning the solar panel to maximize energy output.
It would be a desirable and recognized step forward in the art if there were presented a changeable message display which is capable of 24 hour self-sufficient operation utilizing solar energy as the sole source of power and which, at the same time, provides the high visibility under all types of conditions normally associated only with high energy consuming systems.
Accordingly, it is a primary object of the present invention to provide an improved self-sufficient electrically powered sign panel having a changeable display of reduced power consumption that requires no moving parts.
A further object of the invention is to provide an improved electrically powered sign panel that utilizes low energy consuming electro-optic (E-O) shutter technology in the display pixels.
A still further object of the invention is to provide an improved electrical sign panel that provides low glare, high contrast reflecting/emitting pixels to provide a time variable character matrix of optimal visibility at all ambient light levels.
A yet still further object of the invention is to provide an improved electrical sign panel that uses ambient sensed light controlled LED emitters to optimize visibility.
Another object of the invention is to provide an improved mobile electrical sign panel that uses ambient light sensed control for solar panel disposition.
Other objects and advantages will become apparent to those skilled in the art upon familiarization with the specification, drawings and claims contained herein.